1. Technical Field of the Invention
The present invention relates generally to a power transmission device equipped with a plurality of power split rotors which interlock with each other to transmit power or torque from a power source to a power-driven member, and a power transmission system using the same.
2. Background Art
There are known power transmission devices of the above type for use in hybrid vehicles equipped with a power source implemented by an internal combustion engine and an electric motor, and driven wheels to which the power or torque is transmitted from the power source. For example, the power transmission devices, as used in the hybrid vehicles, typically include a planetary gear train consisting of three rotors: a sun gear, a carrier, and a ring gear to which an electric generator, an internal combustion engine, and an electric motor are connected mechanically. The driven wheels of the vehicle are coupled mechanically to the electric motor. The planetary gear train is so designed that when the torque is applied to the sun gear or the ring gear, it rotates the carrier to turn a rotating shaft of the internal combustion engine, so that the internal combustion engine is started. After start-up of the engine, the torque of the engine is transmitted to the driven wheels through the carrier.
For example, Japanese Patent First Publication No. 2006-308039 discloses the above described type of power transmission device.
The power transmission device, as described above, is so designed that the rotors of the planetary gear train which are connected mechanically to the power source and the driven wheels are fixed, which may result in unsuitable mechanical connections among the power source, the power-driven member, and the power transmission device which leads to mismatching of the gear ratio of a power transmission path between the power source and the power-driven member with running conditions of the vehicle.